Aeroengine titanium alloys such as Ti-6Al-4V experience creep-fatigue loading conditions during the critical fighter aircraft operations. To ensure and enhance the reliable application of such alloys, mechanical behaviour across multiple length scales need renewed attention. Hence, in the present investigation, an attempt has been made to study creep-fatigue damage across multiple length scales (microstructure to component level) using damage mechanics methodology for Ti-6Al-4V alloy. This involves ambient creep, fatigue and creep-fatigue experimentation; identification of various parameters for creep and fatigue models; developing a creep-fatigue model and finally application of this model for damage simulation at specimen, component and microstructure levels. At specimen level, creep-fatigue damage has been obtained from simulations and compared with experimental values. A very good comparison has been observed for the applied maximum peak stress range of 925–975 MPa. The creep-fatigue model has also been successful in mapping damage and identifying critical damage locations in component as well as in the microstructure. © 2018 Elsevier Ltd

S. Ganesh Sundara Raman

Department of Metallurgical and Materials Engineering

Jalaj Kumar

A. Venugopal Rao

Vikas Kumar

Aircraft engines

Aluminum alloys

Creep

Damage detection

Fatigue testing

Fighter aircraft

microstructure

Ternary alloys

Titanium alloys

Vanadium alloys

CREEP FATIGUE

CREEP-FATIGUE DAMAGE

CREEP-FATIGUE LOADING

CREEP-FATIGUE MODELS

Damage mechanics

Experimental values

Length scale

Mechanical behaviour

Fatigue damage

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

International Journal of Fatigue

This study investigates the mechanistic approach to evaluate total stored energy consisting of damage energy (due to voids and microcracks) and deformation energy (due to dislocations). Thermal data obtained by online IRT technique have been employed for this evaluation. The deformation energy is estimated through EBSD analysis. Subsequently, the damage and deformation induced by creep and fatigue have been modeled as functions of applied stress and cumulative plastic strain, individually. By using the data of experimental creep stress and fatigue strain for each creep-fatigue cycle, the contributions of creep and fatigue damage energies have been estimated for creep-fatigue interaction. New fatigue and creep damage parameters have been proposed based on the damage mechanics concepts. Different regimes have been identified and explained with creep and fatigue damage evolution curves. The present approach has also been extended to characterize incremental creep-fatigue interactions. © 2017 Elsevier Ltd

Creep-fatigue damage modeling in Ti-6Al-4V alloy: A mechanistic approach

In the present investigation, microtexture analysis using electron back-scattered diffraction technique has been performed to study fatigue- and creep-fatigue damages and associated deformation structures in Ti-6Al-4V alloy. Special emphasis has been given to low-angle grain boundary configuration and its possible application as a damage indicator. Damage is mostly present in the form of voids as investigated through scanning electron microscopy. Stored deformation energies have been evaluated for the strain-controlled fatigue-, the stress-controlled fatigue-, and the creep-fatigue-tested samples. Stored deformation energies have also been analyzed vis-à-vis total damage energies to quantify the contribution of damages to various samples. A relation between the stored deformation energy and the applied strain amplitude has been proposed in this study. © 2016, The Minerals, Metals &amp; Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Microtexture Analysis and Modeling of Ambient Fatigue and Creep-Fatigue Damages in Ti-6Al-4V Alloy

The present work describes the microstructural features of alloy Ti-6Al-4V during constant stress creep at ambient temperature. Samples tested at 800 and 900 MPa stress levels exhibit the presence of etch-pits and/or voids. The ambient creep strain increases with an increase in applied stress due to higher strain rate sensitivity at higher stresses. A high density of low-angle grain boundaries is noticed in and around etch-pits in the creep-tested specimens due to occurrence of slip. The inverse pole figure obtained by EBSD indicates prismatic texture as the main deformation component in the creep-tested specimens. © 2016, The Minerals, Metals &amp; Materials Society and ASM International.

Observation of Etch-Pits and LAGB Configurations During Ambient Creep of Ti-6Al-4V Alloy

In the present investigation, creep–fatigue interaction was studied in an alpha–beta titanium alloy Ti-6Al-4V at ambient temperature. Stress controlled low cycle fatigue tests were conducted with and without hold times. The hold times were introduced to simulate creep phenomenon. The creep damage was found to be responsible for a large reduction in life of the sample tested with hold time. © 2015, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Creep–Fatigue Interactions in Ti-6Al-4V Alloy at Ambient Temperature

Low cycle fatigue (LCF) damage in titanium alloys has been traditionally assessed based on driving parameters such as stress, strain or hysteresis energy. These mechanical parameters sometimes fail to quantify the true contribution of stored damage energy which is the main cause of LCF damage in these alloys. Hence in the present investigation, thermal evolution captured on-line using lock-in infrared-thermography has been used to characterize low cycle fatigue damage of Ti–6Al–4V under a range of applied total strain amplitudes (0.8–1.8&nbsp;%). The analysis of thermal signatures indicated that the contribution of thermo-elasticity decreased and inelasticity increased with an increase in strain amplitude due to significant change in damage micromechanism from quasi-cleavage to ductile mode. Increase in applied strain resulted into increased fatigue damage and consequently higher temperature increase. An inverse relationship similar to standard strain amplitude-fatigue life equation was established between temperature increase and fatigue life. The damage energy was evaluated using first law of thermodynamics i.e. law of energy conservation. Damage energy increased with an increase in applied strain amplitude. A relationship was also developed between damage energy and strain amplitude. © 2015, Springer Science+Business Media New York.

Journal of Nondestructive Evaluation

Analysis and Modeling of Thermal Signatures for Fatigue Damage Characterization in Ti–6Al–4V Titanium Alloy

Creep-fatigue damage simulation at multiple length scales for an aeroengine titanium alloy

Journal	Data powered by TypesetInternational Journal of Fatigue
Publisher	Data powered by TypesetElsevier Ltd
ISSN	01421123
Open Access	No